1. Field of the Invention
The present invention relates to a heating apparatus for heating a passenger compartment of a vehicle, by using cooling water of a water-cooled engine as heating source, and is preferably employed in a hybrid type vehicle switching both of the engine and the motor as driving force of the engine.
2. Description of Related Art
The hybrid type vehicles have been conceived to reduce the exhaust gas (hereinafter referred to as "emission") containing carbon monoxide, nitrogen oxide or the like which are harmful to a human body, discharged from the engine. More, specifically, the hybrid type vehicle generally runs with a motor driven by an electric power charged in a battery. When the electric power charged in the battery lowers less than a predetermined value, the vehicle runs with an engine to generate electricity and to charge the battery. When the electric power charged in the battery recovers up to the predetermined value, the vehicle runs with the motor again.
That is, by using the motor and the engine as a main driving source and a sub driving source, respectively, a time period during which the engine operates is shortened so that the emission is reduced. Accordingly, to promote the reduction of the emission in the hybrid type vehicle in future, it is necessary to prolong a stopping time of the engine.
Even in the hybrid type vehicle, similar to a conventional vehicle having only the engine as the driving source, a heater core using cooling water of the engine as heating source is employed as heating means for heating air blown out into the passenger compartment. Accordingly, during a heating operation, the cooling water coming from the engine is introduced directly into the heater core, not only when the engine operates but also when the engine is stopped.
However, whether the engine is operating or not is determined by a state of the electric power charged in the battery, and therefore, when the passenger is present in the vehicle such as when the vehicle is running, the engine is occasionally stopped. Accordingly, when the engine as heating source of the cooling water is stopped during the heating operation, the heating capacity is lowered in accordance with the decrease in a temperature of the cooling water, which causes a problem in that it is impossible to heat the passenger compartment effectively entire over the stopping time of the engine. If the engine is restarted while the engine is cold, the emission may increase as compared with when the engine is warm.
The above-described problem is not limited to the hybrid type vehicle. For example, in a conventional vehicle having only the engine as driving source, such a problem occurs when the engine is idling such as when the vehicle is stopping to wait for the traffic lights to change, while the heating operation is continued (i.e., in a rest mode).